At an inlet of a duct and a curved portion of the duct, a flow is disturbed and a flow separation from an inner surface of the duct is likely to occur.
In order to suppress occurrence of a flow separation from an inner surface of the duct, as illustrated in FIG. 20, Patent Document 1 discloses a structure where a flow control plate 3 formed in a form of a lattice is provided at a portion of a duct 2 close to an inlet 2a. The flow control plate 3 is provided so as to extend over an entire cross-section of the inlet 2a of the duct in a width direction and a height direction of the duct.
However, there are the following problems with the structure disclosed in Patent Document 1 above:
Since the flow control plate 3 is provided so as to extend over the entire cross section of the inlet 2a of the duct, a pressure drop caused by the flow control plate 3 is considerably large. Therefore, the structure disclosed in Patent Document 1 is required to be improved such that not only suppression of a flow separation is maintained but also a pressure drop is decreased.